I noted previously that Audacity’s output volume is pretty low. This was confirmed when Dave Jobbings at the Podcast Directory for Educators told me that my submitted podcasts were pretty low.
There’s a good site for this here.
One simple way to get the output volume higher is to select the part of the recording that you want to make louder, then go to “Effects”, then “Amplify”. Bump up the dBs and tick the “allow clipping” box.